A novel alkylating agent, 3-bromo-2-oxo-propane phosphonic acid, will be used to test subunit interaction hypotheses which have been proposed for several dehydrogenases. Specifically, the double negative charge on this reagent at neutral pH will be exploited in attempts to purify enzyme species modified at various fractions of the total number of identical active sites. The binding and catalytic functions of the remaining sites will be examined for evidence of dependence on the function of the modified sites.